1 Answer
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Contextually, Isaiah 49 is describing the return of Jacob/Israel from exile. Verse 49.5:

'And now YHWH says ... to bring Jacob back to him, that Israel might
be gathered to him'

This includes the rebuilding of the city Jerusalem/Zion. Beginning in verse 14:

But Zion said, 'YHWH has forsaken me, and my Lord has forgotten me.'

[YHWH's response] 'Can a woman forget her nursing child, that she
shouldn't have compassion on the child of her womb? They may forget,
but I will not forget you. Behold, I have engraved you on the palms of
my hands, your walls are continually before me. Your builders shall
make haste, your destroyers and those who laid you waste go out from
you.'

The 'walls' are actual walls, which surround the rebuilt Jerusalem/Zion.